Electromagnetic interference shielding in an implantable medical device

Abstract

EMI shields for use in implantable medical devices that include inner and outer metal layers separated by a dielectric layer. When assembled as medical devices, the outer metal layer of an illustrative EMI shield is placed into electrical contact with a conductive inner surface of an associated canister for an implantable medical device.

1. An implantable cardiac stimulus device (ICSD) comprising:
 operational circuitry adapted to sense cardiac activity and provide cardiac stimulus output; 
 a canister formed of a conductive metal and shaped for housing the operational circuitry, the housing having first and second major faces; and 
 an EMI shield comprising an outer metal layer and an inner metal layer with a dielectric therebetween; 
 wherein the EMI shield separates the operational circuitry from one of the major faces of the housing such that the outer metal layer is in electrically conductive contact with the canister. 
 
   
   
     2. The ICSD of  claim 1 , wherein the outer metal layer is electrically isolated from the inner metal layer of the EMI shield. 
   
   
     3. The ICSD of  claim 1 , wherein the inner metal layer of the EMI shield is electrically connected to a reference output of the operational circuitry. 
   
   
     4. The ICSD of  claim 1 , wherein:
 the EMI shield includes an outer perimeter; 
 the inner metal layer covers a major portion of a first side of the EMI shield relative to the outer perimeter; and 
 the inner metal layer does not extend to a pull-back region adjacent the outer perimeter. 
 
   
   
     5. The ICSD of  claim 4 , wherein the pull-back region has a width of about 60 mils. 
   
   
     6. The ICSD of  claim 4 , wherein the outer metal layer extends around the dielectric at the perimeter. 
   
   
     7. The ICSD of  claim 1 , wherein the EMI shield further includes an inner dielectric layer covering a major portion of the inner metal layer and substantially isolating the operational circuitry from contact with the inner metal layer. 
   
   
     8. The ICSD of  claim 1 , wherein:
 a first electrode is disposed on the canister; 
 the ICSD further comprises a lead assembly coupled to the operational circuitry via a header provided on the canister, the lead assembly including at least a second electrode; and 
 the operational circuitry includes high-voltage capacitors and a battery system and is adapted to deliver a stimulus output in the range of more than 50 V in amplitude using an electrode system including the first and second electrodes. 
 
   
   
     9. The ICSD of  claim 1 , wherein
 a first electrode is disposed on the canister; 
 the ICSD further comprises a lead assembly coupled to the operational circuitry via a header provided on the canister, the lead assembly including at least a second electrode; and 
 the operational circuitry includes high-voltage capacitors and a battery system and is adapted to deliver a stimulus output sufficient to achieve cardioversion/defibrillation of a patient into whom the ICSD can be implanted. 
 
   
   
     10. An implantable medical device (IMD) comprising:
 operational circuitry adapted to sense cardiac activity; 
 a canister formed of a conductive metal and shaped for housing the operational circuitry; 
 an EMI shield comprising an outer metal layer and an inner metal layer with a dielectric therebetween; 
 wherein the EMI shield is disposed between the operational circuitry and at least a portion of the canister such that the outer metal layer is in electrically conductive contact with the canister. 
 
   
   
     11. The IMD of  claim 10 , wherein the outer metal layer is electrically isolated from the inner metal layer of the EMI shield. 
   
   
     12. The IMD of  claim 10 , wherein the inner metal layer of the EMI shield is electrically connected to a reference node of the operational circuitry. 
   
   
     13. The IMD of  claim 10 , wherein:
 the EMI shield includes an outer perimeter; 
 the inner metal layer covers a major portion of a first side of the EMI shield relative to the outer perimeter; and 
 the inner metal layer does not extend to a pull-back region adjacent the outer perimeter. 
 
   
   
     14. The IMD of  claim 13 , wherein the pull-back region has a width of about 60 mils. 
   
   
     15. The IMD of  claim 13 , wherein the outer metal layer extends around the dielectric at the perimeter. 
   
   
     16. The IMD of  claim 10 , wherein the EMI shield further includes an inner dielectric layer covering a majority of the inner metal layer and substantially isolating the operational circuitry from contact with the inner metal layer. 
   
   
     17. An EMI shield for use in an implantable medical device (IMD), the EMI shield comprising:
 an outer metal layer; 
 an inner metal layer; and 
 a first dielectric separating the outer metal layer from the inner metal layer; 
 wherein the EMI shield is sized and shaped for placement between operational circuitry of the IMD and a housing for the IMD. 
 
   
   
     18. The EMI shield of  claim 17 , further comprising a second dielectric disposed over a major portion of the inner metal layer, the inner metal layer including a solder pad for attaching a wire thereto. 
   
   
     19. The EMI shield of  claim 17 , wherein the EMI shield includes a perimeter portion and the inner metal layer does not extend to the perimeter portion. 
   
   
     20. The EMI shield of  claim 19 , wherein the outer metal layer wraps around the perimeter portion. 
   
   
     21. A method of manufacturing an implantable medical device comprising:
 providing housing elements including at least first housing element having an inner face and an outer face, the first housing element having a conductive metal surface on at least the inner face; 
 providing operational circuitry adapted to perform methods of the implantable medical device; 
 providing an EMI shield including an outer metal layer, an inner metal layer, and a first dielectric layer therebetween; and 
 assembling the housing elements and the operational circuitry such that the EMI shield separates the operational circuitry from the first housing element and outer metal layer is in electrical contact with the conductive metal surface on the inner face. 
 
   
   
     22. The method of  claim 21 :
 wherein the operational circuitry has a reference voltage output; and 
 the method further comprises electrically coupling the inner metal layer to the reference voltage output of the operational circuitry. 
 
   
   
     23. A method of manufacturing an implantable cardiac stimulus device (ICSD) comprising:
 providing first and second canister sections formed of a conductive metal, each of the first and second canister sections including a major face and sides; 
 providing an EMI shield having components corresponding to each of the first and second canister sections, the EMI shield having an outer metal layer, an inner metal layer, and a first dielectric layer therebetween; 
 providing operational circuitry for the ICSD including a battery, a capacitor block, and control circuitry; and 
 assembling the first and second canister sections, the EMI shield, and the operational circuitry such that the outer metal layers of the EMI shield components are electrically coupled to corresponding interior surfaces of the first and second canister sections, with the EMI shield components placed between the operational circuitry and respective first and second canister sections. 
 
   
   
     24. The method of  claim 23 :
 wherein the operational circuitry includes a reference voltage output; and 
 the method further comprises electrically coupling the inner metal layers of each of the EMI shield components to the reference voltage output. 
 
   
   
     25. The method of  claim 23 , wherein the EMI shield components each have an outer perimeter and the inner metal layer does not extend to a perimeter section having a width of at least 10 mils. 
   
   
     26. The method of  claim 25 , wherein the EMI shield components each have outer metal layers that extend to and wrap around the outer perimeters. 
   
   
     27. An implantable cardioverter-defibrillator (ICD) comprising:
 operational circuitry including a battery, energy storage circuitry, and control circuitry, the operational circuitry configured to monitor cardiac activity of a patient by receiving signals from implanted electrodes and to deliver stimulus to the heart of the patient in response to an identified malignant arrhythmia; 
 a canister including at least some regions of conductive material; and 
 an electromagnetic interference (EMI) shield disposed between the operational circuitry and the canister, the EMI shield comprising an outer metal layer and an inner metal layer with a dielectric therebetween, the EMI shield configured to substantially prevent nonlinear effects during delivery of stimulus. 
 
   
   
     28. The ICD of  claim 27  wherein the EMI shield is configured to limit the occurrence of voltage differentials across air gaps between the EMI shield and the canister.